The present invention relates to an array-type light modulator incorporating flexible thin films to change transmittance of light, an array-type exposing device for use in a UV sensitive material, a visible light sensitive material or an IR sensitive material and a flat-type display unit incorporating the array-type light modulator to cause a phosphor to emit light to perform display.
Hitherto, digital exposing methods for use in a variety of image forming processes include a method using a laser beams, a method using a UV light source and an LCD shutter and a method using a UV light source and an electrooptic crystal shutter.
The method using a laser beam, for example, raster is a scan for relatively moving an image forming member and a laser beam so that successive exposing operations are performed. The foregoing method is able to form a fine image by an image generating function thereof.
The method using a UV light source and an LCD shutter uses change in the optical characteristic occurring when changes in the arrangement of molecules by dint of an electric field of the LCD shutter so as to selectively shield UV rays so that exposure is controlled.
The method using a UV light source and an electrooptic crystal shutter, such as Pockels cell, uses a linear electrooptic effect of electrooptic crystal, the refractive index of which is changed in proportion to the first power of an applied electric field. The Pockels cell is obtained by cutting a parallel and flat plate of electrooptic crystal vertically to an optical axis thereof. An electric field is applied in a direction of the optical axis. Then, birefringence which occurs when a UV ray is allowed to pass in the foregoing direction is used to control the exposure.
A variety of thin and flat display units have been disclosed which are represented by, for example, a liquid crystal display unit, a plasma display unit and a field emission display (FED).
The liquid crystal display unit has a structure that oriented liquid crystal is enclosed and sealed between a pair of substrates each having a conductive transparent film. Moreover, the foregoing structure is held between perpendicular deflection plates. The liquid crystal display unit performs display such that voltage is applied to the conductive transparent film so that liquid crystal is oriented perpendicular to the substrates so as to change transmittance of light emitted from a backlight. To perform full color display or to display a dynamic image, an active matrix liquid crystal panel incorporating TFT (a thin film transistor) is employed.
The plasma display unit has a structure that a multiplicity of electrodes corresponding to an anode and a cathode and arranged regularly are disposed between two glass plates between which a rare gas, such as neon, has been enclosed. Moreover, intersections of opposing electrodes serve as unit pixels. The plasma display unit performs display in accordance with image information to selectively apply voltage to opposing electrodes with which an intersection is specified. Thus, the intersection is caused to perform discharge and emit light so as to excite phosphor with a generated UV ray.
The FED has a structure formed into a flat display tube which covers a pair of panels disposed apart from each other for a short distance to be opposite to each other. A fluorescent film is formed on the inner surface of the displaying panel. Electric field emission cathodes for corresponding unit light emitting regions are disposed on the rear panel. The electric field emission cathode incorporates pointed electric field emission type micro-cathode called an emitter tip having a small size. Display performed by the FED is performed by causing the emitter tip to emit electrons which are then accelerated so that the phosphor is irradiated. As a result, the phosphor is excited.
However, the above-mentioned light modulator, the exposing device and the flat-type display unit have a variety of the following problems.
That is, the structure using a laser beam cannot reduce the size of the apparatus. What is worse, the cost of the apparatus is raised excessively. Since the laser beam is used to perform scanning so as to perform the exposure, exposure of the overall image forming member cannot be performed. Therefore, a multichannel structure cannot easily be constituted and high speed exposure cannot easily be performed.
The structure using the UV light source and the LCD shutter involves transmission of the UV ray to pass through a plurality of transmissive elements which constitute the LCD shutter. Therefore, the efficiency in using light deteriorates. Another problem arises in that the durability of the LCD shutter against the UV ray is unsatisfactory.
The structure using the UV light source and the electrooptic crystal shutter must be applied with a very high operating voltage. What is worse, a two-dimensional array structure cannot easily be constituted because the electrooptic crystal shutter is manufactured by cutting crystal, such as ADP (NH.sub.4 H.sub.2 PO.sub.4) or KDP (KH.sub.2 PO.sub.4).